The use of stellar objects, such as stars and planets, for the calibration and alignment of optical systems is well known. However, the use of stellar objects is often restricted by atmospheric conditions and/or the physical location of the optical system.
As such, the generation of artificial alignment reference points has been employed to overcome the reliance on such naturally occurring references.
By example, in U.S. Pat. No. 3,912,395, entitled "Optical System Calibration Method", Voggenthaler discloses an optical system calibration method that directs a single beam of collimated light through a diffraction grating. This results in the generation of a plurality of diffracted wavefronts, and a creation of an artificial star field which enables a lens to be calibrated to correct the position of objects in a photographed scene, and to thus compensate for distortion.
In U.S. Pat. No. 4,270,044, entitled "Optical Reference Gyro", Elwell, Jr. discloses an optical reference gyro that emits a collimated beam which is directed onto an optical sensor at an objective. A corner reflector 44 is employed to direct the collimated beam. The beam creates an artificial star at the point of incidence of the focal plane of the sensor.
In U.S. Pat. No. 4,021,662, entitled "Laser Target Simulator", Mimms discloses the use of a concave spherical mirror which collimates the light energy from two LEDs and projects the light across the full aperture of a laser seeker. This target simulation technique is employed for evaluating point target tracking systems.
In U.S. Pat. No. 4,712,851, entitled "Positioning Alignment Apparatus and Method Using Holographic Optical Elements", Fusek et al. disclose the alignment of a subject in a space coordinate system. The technique of Fusek et al. employs at least one holographic optical element (HOE) for developing two beams of focussed light whose focal configurations appear in predetermined locations that correspond to the position of the subject in the system.